Quantum computing is an emerging technology that leverages a quantum mechanical phenomenon not available in classical systems (e.g., superposition and entanglement, etc.) to process information. In a conventional computing system, the basic unit of information is a bit, which is a two-state element that can be in either a “one” or “zero” state. In contrast, the basic unit of information in a quantum-computing system, referred to as a qubit, can be in any superposition of both states at the same time (referred to as “superposition states”). Furthermore, many qubits can be in a superposition of correlated states in a way that the system cannot be described as a product of the individual qubit states (referred to as “entangled states”). These forms of qubit states representing the information are not available in conventional (classical) computers. As a result, theoretically, a large-scale quantum computer can solve some problems that simply are not practically feasible using conventional computing approaches. Unfortunately, quantum computers have proven difficult to realize in large scale due.
One attractive avenue for realizing practical quantum computing is “trapped-ion processing,” which relies on electromagnetic fields to confine atomic ions in free space and optical addressing and reading out of the qubits via one or more laser beams. Trapped-ion processing is seen as a potentially enabling technology for large-scale quantum computing and robust quantum information processing (QIP). New trapped-ion protocols that enable scalable quantum computing and long-distance quantum communication have been proposed and successfully demonstrated; however, the size and complexity of conventional ion traps has proven to be a limiting factor in the realization of a practical, large-scale, deployable trapped-ion QIP system.
Recently, progress in microfabricated (surface) traps have demonstrated high performance qubit measurement and quantum gates that outperform conventional manually assembled macroscopic traps. In fact, microfabricated surface traps capable of potentially supporting more than one hundred ions have been demonstrated, with single-qubit properties comparable to those demonstrated in macroscopic traps. As a result, it is believed that such traps represent a major step toward overcoming the scaling challenge faced by quantum computing.
Unfortunately, the use of chip-based ion traps leads to several other challenges, some intrinsic to the chip technology and others simply stemming from the scalable nature of this approach.
One significant challenge arises from the fact that ion traps are subject to anomalous heating, where the ion experiences higher-than-expected motional heating when they are trapped closer to the surface of the trapping electrodes. This will have substantial impact on the quality of multi-qubit gates mediated by the motional degree-of-freedom for the ions. Fortunately, recent studies suggest that in-situ cleaning of the trap electrodes can substantially decrease the heating rate to within an order of magnitude of the fundamental thermal noise limit.
Another challenge for chip-based ion traps is the need to isolate the trapped ions from the background residual gas molecules. As a result, ion traps must be operated at extremely high vacuum levels—typically 10−9 Torr or better. Historically, complex and cumbersome infrastructure has been necessary to achieve such vacuum levels. As a result, the scalability of conventional quantum computing systems that employ microfabricated surface traps remains a challenge.
In addition, a microfabricated surface trap requires a source of ions for loading the trap. Typically, the ions are captured from an atomic plume generated by a source, such as a thermal oven. Unfortunately, the heat generated by conventional sources can interfere with ion-trap operations. By scaling the ion trap system smaller, the distance between the source and ion trap shrinks, further exacerbating thermal coupling between them.
The need for a practical ion-trap enclosure that can support high-vacuum conditions, generation of high-voltage radio-frequency (RF) signals, large numbers of DC signals, enable optical access for one or more laser beams for addressing/reading out trap states, and operation of a source of atomic flux remains, as yet, unmet in the prior art.